The subject matter of the invention relates to the construction and method of fabricating laminated composite structures of the type wherein a plurality of materials are joined together to provide an integral structure having the composite physical and chemical characteristics of the materials utilized. The invention is more specifically concerned with composites predominantly utilizing non-metallic materials such as high strength glass fibers, open and closed cell resin foams and thermosetting resin binders.
Numerous methods and techniques are presently available for making shapes or structures utilizing resin impregnated fiberglass. Typical of such methods are the hand lay-up methods whereby vehicle and boat bodies are made by the laborious process of laying fiberglass sheets within a mold and applying intermediate layers of resin thereto until the requisite thickness is achieved and then allowing the composite to cure within the mold. Another method produces a composite material known as Sheet Molding Compound whereby resin impregnated fiberglass is subjected to high molding pressure in the nature of 1000-2000 lbs. per square inch, and then cured. These and other composite molding techniques have various disadvantages including one or more of the following: slowness of fabrication, high labor content, or expensive tooling particularly where high molding pressures are employed. In common, previous composite molding techniques have limited the structural forms of materials which can be combined to realize a composite structure.
Particular difficulty arises with previous technologies where it is desired to make a composite structure requiring high strength, surface hardness or impermeability and structural rigidity, the latter characteristic which normally requires the part to be of a relatively thick cross-section or otherwise be reinforced.
The present invention is directed to a composite structure which utilizes a lightweight, rigid core element to which a high strength and impervious outer skin is molded. To achieve this result two primary objectives must be achieved. First, the process whereby the high strength outer skin is formed upon the lightweight core element must be accomplished in a way as not to crush the core element. Secondly, the high strength skin must be so bonded to the core element to provide a high shear or peel strength to reduce the possibility of delamination.